Both N-acetyl cysteine (NAC) and 4-hydroxyphenylretinamide (4- HPR) were found to have significant effects on the multiplicity of TPA-induced papillogenesis in male TG.AC mice. 4 -HPR was found to inhibit papillogenesis and the inhibition was only observed if present early in papillogenesis. Follow- up experiments demonstrate that 4-hpr is anti-inflammatory in the early hours after initial TPA treatment. We are evaluating the possibility that 4-HPR stimulates apoptosis of inflammatory cells. It appears from two separate experiments that when fed on top of a soy- based semi-purified diet, NAC at 1.5% and 3.0% of the diet stimulates the multiplicity of these papillomas. This is most interesting because NAC is usually inhibitory to the carcinogenic process- we have identified a paradoxical activity of this antioxidant. This phenomenon does not occur when NAC is fed in casein-based diets. Thus, it appears there is an interaction between NAC and some component(s) of the soy isolate (not occurring in the casein-based diet) which cooperate to cause the increased papilloma multiplicity. A second objective is to test the hypothesis that the modulation of dietary antioxidants at two distinctly different stages of pathogenesis will have opposite effects on the eventual yield of malignant tumor formation. We postulate that minimizing oxidative stress (by dietary antioxidants) in the earliest stages (promotion) of tumor pathogenesis will serve to functionally neutralize the inflammatory component of tumor promotion, thereby eventually translating to a decreased yield of malignant tumors. In contrast, we anticipate that minimizing oxidative stress (thus inhibiting apoptosis) specifically in the period when induced lesions progress from preneoplasia through malignancy will result in a selective advantage for the damaged cells and eventually yield more malignancies. We therefore evaluated this hypothesis using Tg.AC x p53 haploinsufficient mice treated topically with B(a)P to induce skin carcinogenesis. Compared to control diets, NAC feeding was associated with a lower tumor burden (multiplicity) of tumors but stimulated it stimulated their progression to malignancies. Finally, a serendipitous observation from this skin cancer experiment was that NAC feeding was associated with enhanced early deaths, possibly from lymphomas. We have begun an in vivo investigation to confirm and amplify this observation. An analogous investigation in vitro shows that NAC supplementation to mitogen treated splenocytes stimulates proliferation and inhibits apoptosis. Thus we have identified three contexts where the prototypic antioxidant exacerbated tumor progression.